1. Field of the Invention
The present invention relates to a positive electrode for a lithium secondary battery and a method for manufacturing the positive electrode. Further, the present invention relates to a lithium secondary battery.
2. Description of the Related Art
Improvements in output and capacity of a lithium secondary battery which is usable in a portable device, an automotive power supply, or the like are required as portable devices such as smartphones and portable game consoles become widespread and interest in the environment issue grows.
A secondary battery including a lithium secondary battery basically has a structure in which an electrolyte is provided between a positive electrode and a negative electrode. Typically, a positive electrode and a negative electrode each include a current collector and an active material provided over the current collector. In the case of a lithium secondary battery, a material which is capable of occluding and releasing lithium ions is used as an active material for a positive electrode and a negative electrode.
Various approaches to improve the capacity and the output characteristics of a lithium secondary battery have been taken. An increase in the capacity and an improvement in output performance of a positive electrode active material are included in these approaches.
Lithium-containing composite oxide having an olivine structure, such as lithium iron phosphate (LixFePO4 (0<x≦1)), has attracted attentions as a material for a positive electrode active material. Lithium iron phosphate has the following advantages: being formed using iron which is very inexpensive as compared to cobalt (Co) and the like; exhibiting high potential (approximately 3.5 V) as a material in which oxidation and reduction of Fe(II) and Fe(III) occur; having favorable cycle characteristics; having a theoretical capacity of approximately 170 mAh/g and having higher energy density than a conventional material such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2); having a high level of safety; and the like.
It is known that there is a one-dimensional lithium-ion path along the b-axis direction of the crystal lattice of lithium iron phosphate, which is lithium-containing composite oxide having an olivine structure (Non-Patent Document 1).